METAR Viewer

METAR Viewer fetches and decodes aviation weather reports (METARs) into plain English. Search by ICAO code, IATA code, airport name, or even a common misspelling, and get wind, visibility, cloud layers, temperature, altimeter, present weather, and flight category back in a readable form.

It ships in three flavours, all built from this one branch: a Windows desktop app, a macOS desktop app, and an in-game toolbar panel for Microsoft Flight Simulator 2020.

Simulation use only. This project is for flight simulation and hobby use. Never use it for real-world aviation, flight planning, navigation, or weather decisions.

What’s in this repository

main is the single source of truth and contains all three versions at once. Develop and release from this branch; the platform-specific implementations live in their sibling projects and workflows.

All three versions share the same METAR decoding engine (MetarViewer.Core), so a parsing fix benefits every version at once.

Which version do I want?

Version	What it is	Runs on	Release to download
Windows desktop app	Standalone window on your desktop. Nothing to install — one self-contained `.exe`.	Windows 10/11 (x64)	METAR Viewer for Windows 1.0.7
macOS desktop app	Standalone `.app` in a disk image, for Apple Silicon and Intel.	macOS 14+	METAR Viewer for Mac 1.0.0
MSFS 2020 panel [Beta]	Weather panel inside the simulator, opened from the in-game toolbar.	MSFS 2020 on PC	METAR Viewer for MSFS 2020 1.0.1

Each version is published as its own release. The current platform releases are Windows 1.0.7, Mac 1.0.0, and MSFS 2020 1.0.1. Each platform maintains its own version sequence, while the three tags identify builds from their exact release source snapshots. Future coordinated releases create all three tags from the same main commit.

Pick a desktop app if you want to look up weather on its own; pick the MSFS package if you want weather without leaving the cockpit. Installing one does not affect the others.

Windows desktop app

A self-contained single-file executable — no .NET runtime, installer, or admin rights needed.

Download METAR-Viewer-Windows-x64-<version>.exe from the METAR Viewer for Windows 1.0.7 release.
Double-click it.

Windows SmartScreen may warn about an unrecognised publisher because the build is not code-signed. Choose More info → Run anyway if you trust the download.

macOS desktop app

Open the METAR Viewer for Mac 1.0.0 release and download the disk image for your Mac:
- METAR-Viewer-Mac-Apple-Silicon-<version>.dmg for M-series Macs.
- METAR-Viewer-Mac-Intel-<version>.dmg for Intel Macs.
Open the .dmg and drag METAR Viewer into your Applications folder.
Launch it.

The DMG is ad-hoc signed rather than notarised, so on first launch macOS Gatekeeper may refuse to open it. Right-click the app and choose Open, or allow it under System Settings → Privacy & Security.

MSFS 2020 in-game panel

This version runs entirely inside the simulator. There is no separate app, background service, or custom installer — it is a normal MSFS Community package.

The panel asks the simulator for weather first, falls back to the VATSIM METAR API when the simulator has no report, and decodes everything locally.

Download metar-viewer-toolbar.zip from the METAR Viewer for MSFS 2020 1.0.1 release, or grab it from the Flightsim.to page.

A source checkout is not installable on its own. manifest.json, layout.json, and the toolbar registration have to be generated first — see Build from source.

Close Microsoft Flight Simulator 2020 completely.
Open your Community folder. If you do not know the path, start MSFS and use Developer Mode → Tools → Virtual File System → Packages Folders → Open Community Folder, then close MSFS again before copying. Alternatively find InstalledPackagesPath in UserCfg.opt and open its Community subfolder. Do not use Official.
Extract the ZIP directly into the Community folder.
Confirm the package metadata sits at the package root:
```
Community\
└── metar-viewer-toolbar\
    ├── manifest.json
    ├── layout.json
    ├── InGamePanels\
    └── html_ui\
```
If you see metar-viewer-toolbar\metar-viewer-toolbar\..., move the inner folder up one level. Do not copy the repository’s integrations\msfs2020 folder into Community.
Start MSFS 2020, begin a flight, and pick METAR Viewer from the toolbar. It may be hidden in the toolbar overflow menu if you have many panels installed.

For a step-by-step walkthrough, see QUICKSTART.md.

What the panel does

Requests weather from the simulator’s facility service first.
Falls back to the VATSIM METAR API when the simulator has no report or the request fails.
Searches airports through AirportsAPI for names and IATA codes.
Still accepts a direct four-letter ICAO code when airport search is unavailable.
Decodes wind, visibility, clouds, temperature, altimeter, weather, and flight category locally.
Briefly caches successful results to avoid repeated requests.
Remembers the last station when the simulator data-store is available.

An internet connection is needed for airport-name/IATA lookup and the VATSIM fallback. The simulator METAR path still works without them when MSFS has the report.

Troubleshooting

Make sure MSFS was closed while you copied the package, and restarted afterwards.
Confirm manifest.json and layout.json are directly inside metar-viewer-toolbar.
Make sure you copied the built package folder, not the repository or PackageSources.
Temporarily remove other toolbar panel mods if the toolbar is unstable after a sim update.
With Developer Mode on, check Tools → Packages for metar-viewer-toolbar.

The app or panel cannot find weather

Try a direct ICAO code such as EGLL, KJFK, or OMDB.
Check your internet connection for airport search and the VATSIM fallback.
Wait a minute and refresh; public weather services are occasionally unavailable.

Removing or updating the MSFS package

Close MSFS, then delete or replace only the Community\metar-viewer-toolbar folder. Never hand-edit layout.json or manifest.json inside a packaged release.

Repository structure

Every version lives on main as sibling projects in one solution:

src/
  MetarViewer.Core/            Shared parsing, models and services. No UI code.
  MetarViewer.App.Avalonia/    Cross-platform desktop UI -> ships Windows .exe + macOS .dmg
  MetarViewer.App.WinUI/       Alternative Windows-native WinUI 3 UI. Windows-only build.
integrations/
  msfs2020/                    MSFS 2020 in-game toolbar panel (HTML/JS + packagers).
tests/
  MetarViewer.Core.Tests/            Shared-logic tests.
  MetarViewer.App.Avalonia.Tests/    View-model tests for the Avalonia app.

Both desktop projects reference MetarViewer.Core; Core references neither. Any METAR or airport logic worth sharing belongs in Core.

Build and run the desktop apps

Both shipping desktop apps (Windows .exe and macOS .dmg) are built from MetarViewer.App.Avalonia, which runs on macOS, Linux, and Windows:

dotnet build src/MetarViewer.App.Avalonia
dotnet run --project src/MetarViewer.App.Avalonia

MetarViewer.App.WinUI is a Windows-native alternative UI that is not currently shipped in releases. It must be built from Windows:

dotnet build src/MetarViewer.App.WinUI
dotnet run --project src/MetarViewer.App.WinUI

On macOS and Linux, dotnet build MetarViewer.sln deliberately skips the WinUI project rather than failing: it is mapped to the x64 solution platform only, so the default Any CPU build stays green everywhere. Building it directly off Windows fails with NETSDK1100, which is expected.

The WinUI project provides a Windows-native look, but is not currently included in releases and its build has not been verified since the Phase 1 refactor (see docs/PHASE-5-HANDOFF.md).

Local .NET SDK setup

global.json pins the SDK to 8.0.418 with rollForward: latestFeature, which only resolves to an 8.0.4xx SDK. If your system-wide dotnet is a different major version, commands fail with an error that looks like a broken solution file:

The application 'sln' does not exist or is not a managed .dll or .exe
A compatible .NET SDK was not found.
Requested SDK version: 8.0.418

The solution file is fine; the SDK simply cannot be resolved. Install the pinned SDK into the gitignored ./.dotnet directory:

./scripts/bootstrap-dotnet.sh

The script reads the version from global.json, is safe to re-run, and leaves your system-wide .NET installation alone. .vscode/settings.json already points the C# extension and integrated terminal at ./.dotnet, so reload the VS Code window afterwards (“Developer: Reload Window”) for new terminals to pick it up.

From an external terminal, either call ./.dotnet/dotnet directly or export:

export DOTNET_ROOT="$PWD/.dotnet"
export PATH="$DOTNET_ROOT:$PATH"

Then build and test as usual:

dotnet build MetarViewer.sln
dotnet test MetarViewer.sln

Installing the .NET 8 SDK system-wide satisfies the pin without the bootstrap step. CI needs none of this: the workflows use actions/setup-dotnet with dotnet-version: 8.0.x.

Build from source

MSFS 2020 package

The integration lives under integrations/msfs2020. There are two ways to produce an installable ZIP.

SDK build (authoritative). Requires Windows, the current MSFS 2020 SDK, and Node.js. It validates the source, compiles the panel registration into a real .spb, validates the generated package, and writes the ZIP to integrations/msfs2020/Packages/.

Portable build (no SDK). Runs anywhere Python 3.9+ is available, including macOS and Linux, and writes the ZIP to builds/:

python3 integrations/msfs2020/tools/build-community-package.py

This generates manifest.json and layout.json itself and ships the toolbar registration as XML under the .spb filename, which the simulator’s loader generally accepts. It is the quickest path to a ZIP you can drop into Community, but the SDK build remains authoritative.

Panel tests run from integrations/msfs2020 with:

node --test
node tools\validate-source.mjs .

See integrations/msfs2020/README.md for the full maintainer workflow.

integrations/msfs2020/PackageSources/.../metar-core.js is a separate JavaScript implementation of the decoding logic, because the simulator panel cannot load .NET assemblies. Behavioural fixes made in MetarViewer.Core must be mirrored there by hand. The MSFS integration is therefore not a .NET project and cannot be referenced with dotnet add reference; it appears in MetarViewer.sln as a solution folder only.

Releases

Each platform gets its own GitHub Release and maintains an independent version sequence, so the Releases page lists clearly labelled downloads for each track:

Release	Tag	Workflow	Asset	Runner
METAR Viewer for Windows	`win-v1.2.3`	`windows-release.yml`	`METAR-Viewer-Windows-x64-*.exe`	`windows-latest`
METAR Viewer for Mac	`mac-v1.2.3`	`mac-release.yml`	Apple Silicon and Intel `.dmg`	`macos-14`
METAR Viewer for MSFS 2020	`msfs-v1.2.3`	`msfs-release.yml`	`metar-viewer-toolbar.zip`	`ubuntu-latest`

release.yml (“Release all platforms”) is the entry point. Every code push to main, or a manual Actions → Release all platforms → Run workflow, will:

Pick the next patch version independently for Windows, Mac, and MSFS (or use the optional shared version override), skipping any already tagged.
Create win-v*, mac-v*, and msfs-v* in a single atomic push, so the three tags describe the same source commit even when their version numbers differ.
Call the three platform workflows in parallel, each publishing its own release.

The Windows release carries the Latest badge; the other two are published with --latest=false so they do not compete for it. The three platform jobs are independent, so a failure in one still lets the other two publish.

To rebuild a single platform, push just that tag — for example git push origin mac-v1.2.3 — or dispatch that platform’s workflow directly.

Why release.yml calls the other workflows instead of only pushing tags. GitHub does not raise workflow-triggering events for refs created with the default GITHUB_TOKEN, to stop workflows triggering themselves. The retired auto-release.yml pushed a v* tag and expected the tag-triggered release workflow to notice, which never happened — that is why v1.0.3–v1.0.6 were tagged but only ever released by hand. workflow_call invokes each platform workflow in-process, so no event delivery is involved and no personal access token is required.

Support METAR Viewer

If this project is useful to you, you can support its maintenance with a coffee:

License

MIT License. See LICENSE.

README